Copper-zirconium-arsenic alloys



United States Patent 3,107,993 CDPPER-ZIRCONIUM-ARSENIC ALLQYS Matti J. Saarivirta, Plainlield, NJ, assignor to American Metal (Jlimax, linen, New Yorir, N.Y., a c rporation of New York No Drawing. Filed Nov. 6, 1961, Ser. No. 150,162 7 Claims. (Cl. 75-153).

This invention relates to copper base alloys and more particularly to ternary alloys containing copper, zirconium and arsenic. The principal object of the invention is to provide copper base alloys of the copper-zirconium type having improved properties and characteristics for applications requiring high electrical conductivity and good strength properties.

Although recently developed copper-zirconium alloys as described, for example, in US. Patent No. 2,842,438 have met widespread acceptance as filling a long existing need for applications requiring high electrical conductivity and moderately high strength and hardness at room and elevated temperatures up to about 500 C., the need for alloys possessing still better physical and mechanical properties remains urgent due to progressively increasing requirements being imposed upon structural components for various electrical, electronic and other applications.

Attempts to increase the zirconium content in copperzirconium alloys appreciably beyond the maximum solid solubility limit of 0.15% by weight for purposes of enhancing various properties of copper-zirconium alloys have not proven too satisfactory due to the occurrence of inverse segregation resulting generally in poor quality castings. The addition of phosphorus to copper-zirconium alloy systems is flso known in the prior art, such alloy compositions generally consisting of additional ingredients such as iron and silicon said to be useful for facilitating the production of the alloy. The use of phosphorus with or without such additional ingredients in the making of alloys of the copper-zirconium type not only makes it exceedingly difficult to produce material of consistently uniform high electrical conductivity but also results in a product that exhibits free oxide scaling thereby rendering the alloy unsuitable for certain applications.

It has now been found that with the incorporation of a minor proportion of arsenic in the alloy in addition to a relatively larger amount of zirconium sufficient to form two intermetallic phases believed to consist of copper zircon-ide (C11 Zr) and zirconium arsenic (Zr-As) compounds in the alloy, several important advantages are derived thereby. These include (a) refinement of grain structure and improved properties of the alloy particularly in wrought lfODIIl, (b) more economical and efficient utilization of the alloying ingredients, (0) effective solution annealing of the alloy at a lower temperature than heretofore usually required for Cu-Zr alloys, and (d) facilitated production of uniformly sound castings. The aforesaid advantages and benefits are attributable mainly to the combining of arsenic with zirconium to form finely dispersed particles throughout the crystal structure of the ternary alloy. The grain refinement effect of arsenic is such that the use of up to as much as 1% zirconium in the alloy presents no problems or difiiculties in connection with casting of the material and its subsequent processing for development of the superior properties of the alloys.

The alloys of the present invention are characterized by the fact that they contain from 0.2 to 1% by weight of zirconium, from 0.1 to 0.5% by weight of arsenic, the balance being copper with its incidental impurities. It is generally preferred, however, to use from 0.3% to 0.7% zirconium and from 0.15 .to 0.35% arsenic with best results being obtained when the alloy contains about 0.5% zirconium and about 0.25% arsenic, balance copper.

The ratio of zirconium to arsenic should generally be within the range of from 4:1 respectively to about 1.5:1 and preferably about 2:1 so that, after combining of the arsenic to form the ZrAs intermetallic compound, sufficient residual zirconium is made available for forming the also essential Cu Zr phase. Though not limited thereto, the copper base used in making the alloy should preferably be oxygen free when the alloying ingredients are added to the copper melt. pers give better results than do oxygen-containing material such as tough pitch copper. Best results are obtained, however, with copper which is substantially oxy gen-free without requiring treatment with any of the conventional chemical deoxidants. Cathode copper, copper produced in a reducing atmosphere such as OFHC brand copper, in an inert atmosphere, under charcoal cover or in a vacuum are examples of the preferred initially oxygen-free copper base material.

The following are specific alloy compositions coming within and illustrating the scope of the present invention:

Example Zirconium, Arsenic, Copper,

Percent Percent Percent 0. 0. 1O bal. 0. 0. 15 bal. 0. 31 O. 20 bill. 0. 48 0. 18 bal. 0. 50 0. 25 bal. 0. 59 0. bal. 0. 88 0. 23 bal. 1. O0 0. bal.

' The alloys of the present invention are made following conventional alloying practices utilizing a protective gas cover during melting of the copper, alloying and casting operations. By way of illustration, the copper is first melted under argon or other suitable protective gas cover in an alloying furnace such as an Ajax induction furnace using a graphite crucible. With the copper melt at a temperature generally between 1150 and 1300 C., the alloying ingredients are added either successively or simultaneously using appropriate amounts of zirconium and arsenic in any suitable form for alloying purposes. Zirconium and arsenic as metal, sponge or powder and as master alloys of the respective elements with copper are illustrative of some of the materials that may be used in making the ternary alloys of the present invention. After alloying, the melt is stirred, held at temperature for a few minutes following which the alloy is cast into graphite or any other suitable molds.

In connection with the alloying and casting operation, the inclusion of arsenic as an alloying element contributes significantly to facilitating the production of uniformly sound castings despite zirconium contents of the alloy appreciably in excess of 0.15% which usually causes inverse segregation particularly in the larger size castings. By incorporating arsenic in the amounts hereinbefore specified, no difficulties are encountered in producing sound castings notwithstanding a content of up to 1% zirconium in the cast material. Utilization of the zirconium and arsenic is virtually complete with little or no loss of alloying ingredients whereas considerable losses of zirconium are encountered in the production of the binary copperzirconium alloys despite the use of initially oxygen-free copper. V The enhanced utilization of the alloying ingredients not only reduces losses of the alloying ingredients but enables much more elfective control of the alloying process whereby variations in the resulting alloy compositions can be minimized.

Examination of the microstructure of the ternary alloys in the cast condition revealed that arsenic reacts with zorconium forming finely dispersed particles of a zirconium-arsenic compound throughout the lattice. These par- Chemically deoxidized copticles increase in quantity with increasing arsenic until the zirconium-arsenic ratio is between 2:1 and 1:1. At below the ratio of approximately 1.3:1, the structure of the alloy consists only of alpha plus the ZrAs compound. When the arsenic content is insuflicient to combine with all the zirconium, the structure consists of alpha plus Cu lr and the aforesaid finely dispersed Zr--As particles. Accordingly, the ratio of zirconium to arsenic present in the alloy should be at least 1.5:] as previously stated.

In the case of the preferred embodiment wherein the alloy nominally contains 0.5% zirconium, 0.25 arsenic, balance initially oxygen-free copper, approximately one half. of the zirconium combines with the arsenic to form a dispersed phase of Zr-As fine particles, the residual zirconium combining with the copper toform the Cu Zr phase. As previously stated, both of these phases are essential for developing the optimum properties of the alloys comprising the present invention.

Solution annealing of cast material at different temperatures indicated upon microscopic examination of the heated and quenched test specimens that maximum solid solubility of the ZrAs rich phase occurred at about 900 C. With alloy compositions containing at least 0.3%.

zirconium and about one-half as much by weight of arsenic and the balance copper, some Cu Zr was visible in the specimens solution annealed at 900 C. Heating to temperatures over 900 C. resultedin dissolving more of the Cu Zr phase but also caused agglomeration of the arseniccompound forming a low melting point arsenic,- rich eutectic. Although somewhat lower or higher temperatures may be used for solution annealing thealloys of the present invention, best results are obtained in the usual case by solution annealing in a protective atmos phere at a temperature of about 900 C. for a period of approximately 30 minutes. Obviously, the heat treatment time may be varied as from about minutes to an hour or so depending upon the size or thickness of the specimen being treated as well as the temperature actually used. Contrasted with the requirement of a solution annealing temperature of about 980 C. for the binary alloys of-copper-zirconium, it is an important advantage of the alloys of this invention that solution annealing can be efiectively achieved at a substantially lower temperature.

The marked grain refinement attributable to the arsenic content of the new alloy compositions may best be illustrated by comparison of solution annealed specimens of the alloy with and without arsenic but otherwise similar in all respects. For example, specimens of Cu0.5% Zr alloy cold drawn to 0.4132" wire (with 72% reduction in area) and then solution annealed at different temperatures of 800, 850 and 900 C. for 30 minutes were characterized by an average grain size of 0.02, 0.035 and 0.045 mm. respectively. The arsenic-containing alloy consisting of 0.5 zirconium, 0.28% arsenic, balance copper subjected to the same treatment resulted in average grain sizes of 0.005, 0.008 and 0.01 mm. for the specimens annealed at 800, 850 and 900 C. respectively.

In addition to the aforesaid advantages pertaining to the alloying, casting'and solution annealing operations as well as the grain refinement benefits provided by the inclusion of arsenic with zirconium as alloying ingredients of copper, significant improvement of various properties of the material is also obtained upon treatment of the ternary alloy. The effect of arsenic on various properties of the alloy in wrought form is seen from the data presented in Table I below. Listed therein are the properties obtained on test specimens of respective binary and ternary copper-base alloys of the same zirconium content and differing only in respect of the arsenic content of the ternary alloys. All of the test specimens were prepared by solution annealing the material at 900 C. for 30 minutes, quenching, cold drawing to 0.081" diameter wire (90% reduction) and aging at 400 C, for one hour.

It will be seen from the above table that a significant improvement of tensile strength, yield strength, hardness and electrical conductivity is achieved by the inclusion of arsenic as an alloying ingredient. For applications. at v ordinary tempartures requiring high electrical conductivity, the combination of properties possessed bythe copper-zirconium-arsenic alloys comprising the present invention are superior to any of the heretofore available alloys of the copper-zirconium type including the aforeunentionsd copper-zirconium-phosphorus alloys with or without iron, silicon, etc. The arsenic-containing alloys additionally possess good scale adherence qualities male, ing the material suitable for, applications in which free oxide scaling is objectionable.

The copper-zirconium-arsenic alloys herein described are amenable to extensive hot and/or cold working up to reductions of or more with no difliculty. Aging may be carried at temperatures of from 350 to about 475" C. for varying periods of time ranging from 10 minutes to 2 hours depending on the size or thickness of the material being treated. Preferred practice consists of aging the material at about 400 C. for a period of approximately one hour.

Since the response of the copper-zirconium-arsenic alloys, like that of the CuZr binary alloys, to precipitation hardening is slight, the optimum properties are developed by solution annealing, quenching, working and aging the material. With such treatment and using the herein disclosed amounts of zirconium and arsenic, up to 75,000 p.s.i. tensile strength, over 10% elongation and 90% I.A.C.S. electrical conductivity are obtained. The arsenic addition is thus seen to enhance the tensile strength by as much as 7,000 p.s.i. and electrical conductivity by about 7% with the other properties being at least as good or better than those of the corresponding copperzirconium binary alloys. With slight overaging of the, alloy, electrical conductivities of I.A.C.S. or even higher are readily obtained. i

The binary copper-zirconium alloys are known to .re-. tain their properties at relatively high temperatures. In r order to compare the high temperature properties of the binary and ternary alloys, specimens of representative alloys containing 0.5 Zr, balance Cu and 0.5% Zr, 0.25% As, balance Cu were tested at 400 C., the material being'first treatedas follows: (a) solution annealed at-900 C. for 30 minutes, (b) quenched, (0) cold rolled to 0.388" diameter rod with 53% reduction in area, and (d) aged at 375 C. for one hour. The high temperature properties measured at 400 C. are summarized in Table II.

It will be seen from the data listed in the above table that the high temperature properties of the binary and ternary alloys are quite similar with the arsenic-containing ternary alloy having slightly higher strength properties whereas the binary alloy is slightly more ductile. By virtue the aforementioned superior properties of the alloys of the present invention for application at ordinary temperatures coupled with high temperature properties at least as good as heretofore attainable with any of the prior art alloys of the copper-zirconium type, as new and novel alloys herein described constitute a significant advance in the art.

While the present invention as to its objects and advantages has been described herein in relation to specific embodiments thereof by way of illustrating the various benefits resulting from the incorporation of controlled amounts of arsenic in alloys of the copper-zirconium type, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

I claim:

1. An alloy of copper, zirconium and arsenic which consists of from 0.2 to 1% by Weight of zirconium, from 0.1 to 0.5% by weight of arsenic, balance copper with normally associated incidental impurities.

2. An alloy of copper, zirconium and arsenic which consists of from 0.2 to 1% by weight of zirconium, from 0.15 to 0.5 by weight of arsenic, balance copper, said copper being initially oxygen-free copper prior to its being alloyed with said zirconium and arsenic.

3. An alloy of copper, zirconium and arsenic which 6 consists of firom 0.2 to 1% by weight of zirconium, 0.15 to 0.5 by weight of arsenic, balance copper, said cop per being initially chemically deoxidized copper prior to its being alloyed with said zirconium and arsenic.

4. An alloy of copper, zirconium and arsenic which consists of from 0.2 to 1% by weight of zirconium, 0J1 to 0.5% by weight of arsenic, balance copper, said zirconium and arsenic respectively being present on a weight basis in the ratio of from 4:1 to 1.5: 1.

5. The alloy of claim 4 wherein the zirconium to Msenic ratio is about 2:1.

6. An alloy of copper, zirconium and arsenic which consists of from 0.3 to 0.7% by Weight of zirconium, from 0.15 to 0.35% by weight of arsenic, balance initially oxygen-free. copper, said zirconium and arsenic respectively being present on a weight basis in the ratio of at least 2:1.

7. An alloy of copper, zirconium and arsenic which consists of about 0.5% by weight of zirconium, about 0.25% by weight of arsenic, balance initially oxygenfree copper with incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 2,842,438 Saa-rivirta et 'al. July 8, 1958 OTHER REFERENCES Butts: Copper the Metal, Its Alloys and Compounds, ACS Monograph Series No. 122. Reinhold publishing Div., New York, 1954, pages 124 and 125. 

1. AN ALLOY OF COPPER, ZIRCONIUM AND ARSENIC WHICH CONSISTS OF FROM 0.2 TO 1% BY WEIGHT OF ZIRCONIUM, FROM 0.1 TO 0.5% BY WEIGHT OF ARSENIC, BALANCE COPPER WITH NORMALLY ASSOCIATED INCIDENTAL IMPURITIES. 